Engines may use various forms of fuel delivery to provide a desired amount of fuel for combustion in each cylinder. One type of fuel delivery uses a single centrally located injector to provide fuel to one or more cylinders. Another type of fuel delivery uses a port injector for each cylinder to deliver fuel to respective cylinders. Still another type of fuel delivery uses a direct injector for each cylinder.
Further, engines have also been described using more than one injector to provide fuel to a single cylinder in an attempt to improve engine performance. Specifically, in US 2005/0155578 an engine is described using a port fuel injector and a direct injector in each cylinder of the engine.
Another approach utilizing multiple injection locations for different fuel types is described in the papers titled “Calculations of Knock Suppression in Highly Turbocharged Gasoline/Ethanol Engines Using Direct Ethanol Injection” and “Direct Injection Ethanol Boosted Gasoline Engine: Biofuel Leveraging for Cost Effective Reduction of Oil Dependence and CO2 Emissions” by Heywood et al. Specifically, the Heywood et al. papers describes directly injecting ethanol to improve charge cooling effects, while relying on port injected gasoline for providing the majority of combusted fuel over a drive cycle.
However, the inventors herein have recognized a disadvantage with such approaches. In particular, systems using a direct fuel injector may have several issues. First, direct fuel injection may increase system cost. Second, when using a high-pressure fuel pump, a reduction in fuel economy may be experienced due to increased parasitic losses. Third, it may be difficult to package a direct injector in some engine configurations, thus resulting in compromised valve sizes, valve angle, intake port shape, injector targeting, or other engine design parameters.
In still another example approach, port injectors have been used with open valve injection in an attempt to increase charge cooling and thus improve fuel economy. However, the inventors herein have recognized that such systems typically provided benefits over only a limited range, such as wide-open throttle conditions. Further, this benefit may be reduced by the need to provide acceptable performance under other conditions, such as acceptable combustion under low fuel flows, acceptable cold starting operating, and acceptable transient fuel response typically performed with closed-valve injection.
To address these issues, yet still provide improved engine performance, a system for an engine is provided, the system comprising: a cylinder located in the engine; a first port injector for injecting a first fuel into said cylinder; and a second injector outside said cylinder for injecting a second fuel into said cylinder.
In this way, it is possible to achieve improved charge cooling operation, thus enabling increase compression and/or boosting while reducing knock limits, and at the same time avoid disadvantages with direct injection systems. Further, by utilizing multiple injectors, it may still be possible to achieve improved charge cooling with one injector designed for open valve injection, while another injector may be designed for closed valve injection.
In another approach, a system for an engine is provided, the system comprising: a cylinder located in the engine; a first port injector for injecting a first fuel into said cylinder; a second port injector for injecting a second fuel into said cylinder; a valve coupled to an intake of the engine; and a controller to adjust said valve to reduce airflow around one of said injectors when said one injector is not injecting fuel.
In this way, by reducing airflow in a port when the injector is not injecting fuel, it is possible to maintain acceptable air-fuel mixing of the fuel from the other injector. Further, such an approach may provide improved packaging compared with twin-spray injectors that may require a more central injector location between the ports, making it more difficult to package two injectors per cylinder.